Due to Applicants' development of a method for the fabrication of flexible, ultra-thin, ultralight substrates, solar cells may now be manufactured by depositing layers of thin film semiconductor alloy material thereupon. Such solar cells are noteworthy in that they exhibit (1) increased operational reliability, (2) increased operational efficiency, (3) increased yields, and (4) have a markedly reduced number of surface defects. Additionally, the solar cells, so produced, are correspondingly thin, lightweight, flexible, and rollable. The solar cells are thereby susceptible to a host of novel applications not previously possible with crystalline solar cells.
Single crystal photovoltaic devices, especially crystalline silicon photovoltaic devices have been utilized for some time as sources of electrical power because they are inherently non-polluting, silent and consume no expendable natural resources in their operation. However, the utility of such devices is limited by problems associated with both the manufacturing and the inherent physical constraints thereof. More particularly, single crystal materials (1) are difficult to produce in sizes substantially larger than several inches in diameter, (2) are thicker and heavier than their amorphous counterparts; and (3) are expensive and time consuming to fabricate.
Recently, considerable efforts have been made to develop systems for depositing amorphous semiconductor materials, each of which can encompass relatively large areas, and which can be doped to form p-type and n-type materials for the production of p-i-n type photovoltaic devices which are, in operation, substantially equivalent to their crystalline counterparts. It is to be noted that the term "amorphous", as used herein, includes all materials or alloys which have no long range order, although they may have short or intermediate range order or even contain, at times, crystalline inclusions.
Unlike crystalline silicon which is limited to batch processing for the manufacture of solar cells, amorphous silicon alloys can be deposited in multiple layers over large area substrates to form solar cells in a high volume, continuous processing system. It is now possible to continuously prepare amorphous silicon alloys by glow discharge or vacuum deposition techniques, said alloys possessing (1) acceptable concentrations of localized defect states in the energy gaps thereof, and (2) high quality electrical and optical properties. Fluorine introduced into the amorphous silicon semiconductor layers operates to substantially reduce the density of the localized defect states therein and facilitates the addition of other alloying materials, such as germanium.
As disclosed in previous patents of Applicants' assignee, a substrate may be continuously advanced through a succession of deposition chambers, wherein each chamber is dedicated to the deposition of a specific layer of semiconductor alloy material. In making a photovoltaic device of p-i-n type configurations, the first chamber is dedicated for depositing a p-type semiconductor alloy, the second chamber is dedicated for depositing an intrinsic amorphous semiconductor alloy, and the third chamber is dedicated for depositing an n-type semiconductor alloy. Since each deposited semiconductor alloy, and especially the intrinsic semiconductor alloy, must be of high purity, every possible precaution is taken to insure that the sanctity of the vacuum envelope formed by the various chambers of the deposition apparatus remains uncontaminated by impurities, regardless of origin.
The instant patent application relates to specific applications to which such mass-produced, ultrathin, ultralight, flexible solar cells may be put. These uses as well as further objects and advantages of the instant invention will become apparent from the following description of the preferred embodiments, when that description is taken in combination with the accompanying drawings and claims.